I actually asked my uncle Steve -- an astrophysicist -- this question once, in relation to ElfQuest's World of Two Moons, and he said that the simple answer is that the more moons you have, the smaller the moons have to be, so the less gravitational force they exert.  This means smaller tides that happen more frequently.  So basically the difference between low tide and high tide is lessened, and you have more high and low tides per day.

Since the Sun also exerts a tidal influence, about half that of the moon, the smaller moons will be overwhelmed by the solar influence very quickly.  So you can easily justify having Earth normal tides by simply saying "the moons are too small to overcome the solar influence."

I'd also recommend picking up the  The Writer's Guide to Creating a Science Fiction Universe, or a similar reference.  Very useful stuff for anyone who worries about science in their game.

Quote from: Jackalope;240994I actually asked my uncle Steve -- an astrophysicist -- this question once, in relation to ElfQuest's World of Two Moons, and he said that the simple answer is that the more moons you have, the smaller the moons have to be, so the less gravitational force they exert.  This means smaller tides that happen more frequently.  So basically the difference between low tide and high tide is lessened, and you have more high and low tides per day.

Ummm. No. While that may be true of a majority of collision moons, captured moons can easily take on some very eccentric orbits similar to orbits of comets that swing into the solar system from the oort cloud. With this, One would have long periods of years where the tides are relatively stable, followed by short spans of months when the moon is in close orbit containing extreme tides that extend the tidal zones significantly from the established norm.

QuoteSince the Sun also exerts a tidal influence, about half that of the moon, the smaller moons will be overwhelmed by the solar influence very quickly.  So you can easily justify having Earth normal tides by simply saying "the moons are too small to overcome the solar influence."

Binary and Trinary solar systems would also have some interesting tidal variations.

Quote from: Koltar;240945John - not all of us were Physics majors - okay?

- Ed C.

And some of were Ed.

Good stuff John.

Edit to add: That last paper has all manner of goodness in terms of setting possibilities.

Bill

I'm no physics major, but I've got a physics-minded brother who loves this stuff.  He can lend a hand in interpreting this.  Thanks, John!

Quote from: HinterWelt;241082Good stuff John.

Years ago, when I first read an article about the moon formation simulations producing multiple moons about a third of the time, I send Robin Canup an email asking her about what happened to the two moons and she had a research assistant send me that paper in hard copy.  I'm glad it's online now.

Quote from: Koltar;240945John - not all of us were Physics majors - okay?

That's why I provided a summary of the issue first, and then the papers.  The papers were for people who wanted to see the support for what I was saying.  Again, the bottom line is that multiple large moons will generally gravitationally interfere with each other.

Quote from: GameDaddy;241012Ummm. No. While that may be true of a majority of collision moons, captured moons can easily take on some very eccentric orbits similar to orbits of comets that swing into the solar system from the oort cloud.

I'm not sure that anyone has gotten a captured moon scenario to work for a moon planet pair like the Earth-Moon system.  When the masses of the two bodies are that close, the potential moon just doesn't slow down enough to be captured.

Aeia, my fantasy world has three moons. According to legend they are houses of great spirits that watch humanity (positive spirits) because when all three are in the eky their relfected glory leaves a bit less fearful darkness than the night without them. Tides (and storms) are fiercer than on Earth, and mountains are often higher in comparison to "flat" lands.  Now "why" there are three moons in a reltively "realistic" fantasy scene, is because I like them, and feel this is different. The gravity dymanics are simply not a concern to the coolness of it all.

Quote from: Silverlion;241356Now "why" there are three moons in a reltively "realistic" fantasy scene, is because I like them, and feel this is different. The gravity dymanics are simply not a concern to the coolness of it all.

You know what? Thanks for reminding me about that. Seriously. Sometimes I get so caught up in plausibility that I often forget that the imagination should be about cool shit, not scientific mojo (at least not all the time). Huh. I get so wrapped up in my own bullshit that I forget that multimple moons = cool and science be damned.



-=Grim=-

Quote from: GrimJesta;241737and science be damned.

The first rule of good writing!

Quote from: GrimJesta;241737You know what? Thanks for reminding me about that. Seriously. Sometimes I get so caught up in plausibility that I often forget that the imagination should be about cool shit, not scientific mojo (at least not all the time). Huh. I get so wrapped up in my own bullshit that I forget that multimple moons = cool and science be damned.



-=Grim=-

You could also justify it with some kind of crazy super sorcery/science- which would make a great adventure hook later on.

"The blood crystals are tainted, soon the moon will crash into the sea and destory us all!"
"Gods of Rimjohb! We'll have to venture into the Klotswamp and steal some... er... fresh crystals!"

Would a "Death Star" style space station the size of our moon screw up a planet's gravity well? Kinda like a regular moon would?

-=Grim=-

Quote from: GrimJesta;243680Would a "Death Star" style space station the size of our moon screw up a planet's gravity well? Kinda like a regular moon would?

-=Grim=-

Depends a lot on its mass. I presume since the Death Star moved, and since spaceships in Star Wars have gravity that they use some form of Anti-Grav/Grav devices; that is, if I cared about explaining it with SCIENCE!

The death star also was, a lot hollow, as you can tell by the one destroyed at Endor.

Quote from: GrimJesta;240940AHHHHHHHHHHHHHHHHH! MATH! *sign of the cross with fingers* EVIL! HISS!

-=Grim=-

Dude. You ask a question that roots straight into hard astrophysics; you don't get to hiss at math...

Bottom line, though, what folk have said here is solid. You don't get multiple large moons around an earth sized planet. You hardly ever get ONE large moon around an earth sized planet - the Earth/moon system is something of a freak show in that regard. When you get more than one, they eventually screw up each other's orbits. Sooner or later one gets pushed inside the Roche limit and gets torn apart. This happens with smaller moons too, it just takes longer.

Someone mentioned highly elliptical orbits as a workaround, but they aren't any more stable - if anything, less.

Now I'm wondering if you can have a ring of equal sized moons in stable orbit around a planet. It might self-synchronize. But it would *scream* "artificial construct".

For the curious - if you like the moon, enjoy it while you can. Eventually it ends up inside earth's Roche limit - millions to billions of years, I think - and shatters. Earth gets a ring at that point, except of course for the massive moon chunks that pelt the planet, probably wiping out all life. Or so I read a couple decades ago; they might have more accurate models now.

Quote from: Ikrast;244133Dude. You ask a question that roots straight into hard astrophysics; you don't get to hiss at math...

Hrmm. Well played. You win this round. I was so proud of my Lugosi-inspired hiss and everything.

I thought the moon was moving away? Or is that Roche thing further out?

-=Grim=-